1. Field of the Invention
This invention relates to electric motors, and in particular to direct current motors of the class suitable for use in toys, portable home appliances and the like. The invention is even more particularly directed to improvements in such a direct current motor of the type wherein each commutator segment has a surface arranged at right angles to the motor shaft for sliding contact with brushes.
2. Description of the Prior Art
In a commutator motor of the above specified type, the brushes are usually riveted onto an end cap of a cylindrical motor casing or frame, in such a way that the contact portions of the brushes are resiliently urged against the commutator segment surfaces disposed opposite to the end cap. The motor of this type is easier to assemble, and the brush contact portions can be urged under constant pressure against the commutator.
If, however, each brush of such a commutator motor is fastened onto the casing end cap by a single rivet only, the brush is easily loosened by motor vibrations or suffers angular displacement due to the rotation of the commutator in sliding contact therewith. The loosened or displaced brushes will not make proper contact with the commutator and will thus shorten the life of the motor.
The fastening of each brush with two or more rivets is also undesirable because it necessitates extra time and labor for assembling. Moreover, the brush, which is extremely small in size, will suffer a decrease in strength if two or more rivet holes are formed therein.
It is another problem with the prior art commutator motor of the type under consideration that the contacting surfaces of the commutator and brushes are often not maintained in a proper state of lubrication. Since the commutator surfaces for sliding contact with the brushes are flat and are arranged at right angles to the motor shaft, the grease or the like applied on these surfaces tends to dissipate readily because of the centrifugal force produced by the rotation of the commutator. When not properly lubricated, the brushes made of phosphor bronze, brass or like material are particularly easy to wear out before the expected lifetime of the motor.
A further problem to be considered with the prior art commutator motor of the type in question concerns the installation of the commutator on the motor shaft in a predetermined angular position relative to the armature. Heretofore, for this purpose, one of the two disc-like insulators on opposite ends of the armature core has been formed to include a positioning boss or like projection which is to be received in a hole in the commutator or in some other member arranged intermediate the armature and the commutator. Such a positioning boss, however, is susceptible to breakage during assembling or handling, because the armature insulators are usually made of paperboard or similar material.